We saw drop-off in the RE71R during the GRM test, but not the Rival-S. That was on my CRX.

On the Miata with 225 Rival-S, I am cooking the rear tires after a few hard laps. Backing off brings them back, though. Saw the same thing at NCM on the west course (not full). These are both shorter courses with lots of turning Tracks with longer straights would likely provide more cooling. For example, I had no issues at COTA.

Getting back to this...big stuff coming soon, but here's a snippet that will helps others doing this same swap...

The K-series MAP sensor is designed to fit in a hole that is pretty deep, sealing against an o-ring. If the metal is thin, the o-ring does not seal perfectly. The metal in the GE intake is relatively thin.

I had a problem start to surface recently at COTA when the car began running super rich during the last session. I limped it home and eventually discovered MAP readings that were a little lower (less vacuum) than I had been seeing. I fixed it by installing a second o-ring around the base of the sensor “stub” and using a washer on the bolt to match the o-ring height. This did two things: 1) it set the standard o-ring depth shorter, and 2) what the standard o-ring does not seal, the second one does. I also put some sealer on the bolt threads since that penetrates the manifold as well.

https://www.miataturbo.net/attachmen...ine=1451568179

Happy New Year!! :party:

Remember this?

Solution => We are fitting 285/30-18 Bridgestone RE-71R's on 11's by tubbing the inner fenders and using a wide-body kit from DG Motorsports (AWR source).

This is a new size for that tire, due 3/1. In the meantime, we'll use 255/40-17 on 10's.

Proof of concept comes from the Wootton SSM autocrosser seen below in black using the same flare kit around 285 Hoosiers in front, and 315's on 12 in the rear. Rules disallow tubbing for that car, so he makes up for the 25" diameter by jacking up the perch height an inch. He's local, so I have studied it carefully.

The white car (Steve Garnjobst's XP autocrosser) is an example of a no-rules solution with tubbed inners. Not pretty, but very functional. Allows the suspension to have the same travel as with the typical 23" tall tire. You'd still have the other 1" higher ride height from chassis to ground, so Steve also moved all of the suspension pick-up points up an inch to get that back too. We will not be going that far...at least at this point.

While I could do this myself, it's being farmed out to someone who can make it pretty...since this car will see some more Optima event exposure in 2016. Apex Auto Works in Houston will do the fab. They do great race car construction, as well as paint and body...and vinyl is what they originally cut their teeth on. So we have many options on final finish. They have obtained a donor chassis (seen here in red) to cut out inner fenders that will then be blended onto mine about an inch or so up. Should make it look much more stock appearing.

Glass parts are built and enroute. Car goes under the knife in a week, with the goal to display it the end of January at the GRM tent at the Rolex 24 in Daytona.

PS: For non-200tw events, you can imagine the possibilities of slicks that we can run with so much room for activities.

Surprised the white car didnt move the shock pickup points as well. Or at least move their tubing most of the way to the shock top mounting holes, thats where the worst of the interference already is with fitting manly tires.

Project Big Wheel has begun.

https://www.miataturbo.net/attachmen...ine=1452576999

That moment when somebody takes a sawzall to your pride and joy...

https://www.miataturbo.net/attachmen...ine=1452576999

After the tubbing and flares are complete, we'll be converting to a 5x114.3 pattern using this method: MiataV8 Conversion: Five Lug Conversion

That gets a better bearing in the front, and a super easy five-bolt hub swap in the rear. I'm also investigating a couple of other front hubs to reduce the machining effort, but the FD RX7/Probe/MX6 hub with sleeve is a good known quantity.

That decision was made when we weighed Wootton'scustom 4x100 CCW wheel and discovered it was 26 lbs. Instead, we'll be using an off-the-shelf Enkei RPF1 18x10.5 ET15 5x114.3 that weighs 19 lbs for half the price, and available with no waiting.

Meanwhile back at the ranch...Andrew Keisler is working on a five-lug version of his front drop spindles for me.

This is just awesome. Can't wait to see the final product.

With the traction problem resolved, the next logical step is more power right? Love this build, I can't wait to see how it'll stack up at this years One Lap.

Nope...bigger brakes.

I suspect that the additional leverage of the 25" tall tire (vs 23) will overwhelm the 11.75 front rotor/Wilwood combo. Hope not, but it would not surprise me.

I have to do different hats anyway for the five-lug conversion...

:likecat:
https://www.miataturbo.net/attachmen...ine=1452623629

Richard does good work. I have had 3 cages built by him and all turned out well made. Based on the builds I have seen him and Ronnie do, the car is in good hands.

faeflora just got a random erection

God damn Honda kids finding out about Miatas and ruining them with their big rims and VTECs.

Ugh.

:giggle:

Serious question: Is this all about brakes? Why would you go up to a 17" wheel when there are 15X10s and such available at much lower weight?

Its about width and tire selection. Nobody makes anything bigger than a 225 in sticky street tires.

I see my guess was too close on the FB page?

It boggles my mind that a performance-oriented carmaker like Mazda (Zoom-Zoom) has not yet produced a dual-lobe cammed engine.

^^ This (clarified in bold).

One Lap uses a 200tw restriction as one of its few rules. You also have to finish the entire event on one set of tires...with 2/32nds remaining.

The fastest 200tw tires right now for a 3-lap time trial are the Rival-S and the RE-71R. The former comes in a 225/45-15, but not the latter. Further, the Rival-S is not good in deep water, whereas the RE-71R is amazing (see my GRM deep water testing sidebar in the track test article).

So ultimately, I wanted to find a way to run the RE-71R in sufficiently large enough size to put all the power down in 3rd, and with enough meat to not wear out during the week. 255/35-18 (or 255/40-17) would probably be enough, but with just a little more effort, I can also fit the new 285/30-18. Both are close to 25" tall and require massive fender work. I have the 255's on the way now and will compare them to the 285 once those are released. I'll run whichever is faster.

I mentioned it a bunch on mnet when everyone was whining about "y only 155hp! honda makes 200hp out of 2 litre!!", but it's worth repeating that Honda's the largest engine manufacturer in the world, had an F1 team and is getting back into developing F1 motors, and has a massive motorcycle business with the history to go with it, as well. Not to forget that Honda is one of the larger auto manufacturers and Mazda is comparatively quite small (and fragile when they keep betting the farm on the rotary).

They just have the R&D and history that Mazda doesn't. The MZR/L series is undeniably a good motor, especially the DISI; however, the K series motor is a contemporary equivalent, and it's just heads and shoulders above Mazda's powerplant efforts.

This project is awesome, and i'm sure the grip will be amazing. But damn, 18's look ugly as sin on a miata.

Personal preference.

I would still rock them for the grip :)

Also in for handling feedback, as historically heavier wheels means a worse ride/handling.

Toyota has also had dual-lobe cams for over a decade and a half. So there's two versions that Mazda could have copied.

Of course, the "right" answer is the infinitely variable BMW Valvetronic.

But we're getting a little off-topic now...

...and it's done.

https://www.miataturbo.net/attachmen...ine=1454022748

Lots of hours, lots of creativity. Apex Auto Works really knocked it out of the park.

Those are 255/40-17 Dunlops on 10" wide XXR's. We'll be doing the five-lug conversion next week so we can mount the 255/35-18 RE71's on 18x10.5 ET15 RPF1's...and later the 285/30-18 when available in March.

I'm at Daytona for the Rolex 24 where we are displaying the car at the GRM tent.

You can see more pics by going to the One Lap Miata FB page and also Apex Auto Works. I'll post under the cover shots as I get bandwidth.

Next thing you know everyone is going to say XXR's are the fast thing around the parking lot. :rofl:

Reminds me of:


https://www.miataturbo.net/attachmen...ine=1454027192

Any plans to change the diff ratio in order to make up for the taller tire? Or is the answer just more power...

Its a track car...you just shift in different places.

I didn't realize this was done in Houston. Holy crap I want to see this!

I think it looks really intense

and with how clean everything is, you automatically start suspecting that the car is fast, and not just some rtard stancebro

Were the shock mounts moved?

No.

Here's the front inner tubbing from the top. OE metal was pie-cut, pushed up and in on either side of the shock, about which the tire rotates, and then new fill metal welded in. Good luck finding the seams.

https://www.miataturbo.net/attachmen...ine=1454262654

https://www.miataturbo.net/attachmen...ine=1454262654

Love the cruise control.
Beautiful build.

Man, the work those guys did on those tubbed fenders is beyond belief. I'm not sure I've ever seen that done that well before. The wheel choice 100% makes sense for your use of the car. When I first saw that you were doing it, I kinda thought the car would look silly, but honestly it looks really good.

Can't wait to see you take on the OLOA group with this thing.

Agreed. I got to see the car in person at the 24 this past weekend and I was blown away. If it was your first time seeing the engine bay of an NB, you wouldn't even be able to tell the inner fenders had been modified.

Those of you following on FB have seen a hint of this, but I'm finally pulling the motor to investigate.

This is my "good" motor. A pro-built sleeved shortblock, with CNC-ported head...and my usual cams and such. Manley rods with ARP bolts. Made about 300hp to the wheels in my CRX. Low hours, never money-shifted. Happened at COTA in T7 after a 4-3 downshift ending up at about 7000rpm. Rev limiter had been reduced from the usual 8500 to 8200 for the day to reduce stress on the motor. Fresh oil change with Redline 30w Racing. Datalogs look normal, save the knock sensor spikes when the things came apart.

I de-clutched immediately when I felt it go, and it appears to have stopped rotations quickly. Fingers crossed that the head is undamaged.

Pulling the motor now...here's the first pics...

https://www.miataturbo.net/attachmen...ine=1457486616

https://www.miataturbo.net/attachmen...ine=1457486616

https://www.miataturbo.net/attachmen...ine=1457486616

As you can see, the rod bolts are broken. First time I've seen that in any of my K builds/failures.

At this point, I am putting the original spare stock TSX motor back in until I get to the bottom of the issue at hand.

I've also spent some time over the last two weeks setting up Plan B...killer deal on something special fell into my lap. Something VERY special.

PS: I have a complete spare pro-built sleeved shortblock, and another CNC'd head on the shelf. But none of that is going in the car until I am confident that I have identified the weak point and fixed it.

Bad rod bolts? Doesn't sound like anything you did.

Assuming those are Carrillo H's with ARP bolts, possible but not very likely. If they were CARR bolts, impossibru

Assembly error?

As stated in my post with the pics => Manley H-beams, which come standard with 3/8" ARP 2000 bolts.

Shortblock assembly done by 4 Piston Racing.

Once I get it out and apart, I'll have a look at the bearings and try to get a closer look at the bolt fracture surface.

Reading, meh. 4 Piston Racing is not a likely source of an assembly error. Spun to 8200, I would think the 3/*'s bolts would survive, particularly as it sounds like a combo you have previous experience with. Too bad the logging wasn't up and running yet, damn.

Yep...logging of oil pressure and temp was on the list, but not yet executed. Kicking myself for that one. Hoping there is some evidence on the other bearings one way or the other. I'll also be checking the other rod bolts with a stretch gauge.

4Piston suggests that the Manley rod is good to 9000+ rpm in this application. And I have spun that high in an autocross situation for a brief moment. Heck, I've spun a 4Piston built K20 (shorter stroke than K24) with the same rods to 9500 rpm in an autocross with no ill effects.

Although Andy and I have talked about this in depth already, I just want you all to know that we're here to support him and dig into any issue that could have possibly stemmed from anything on our end. I think it's unlikely, but of course we don't want to jump to conclusions.

Of course its a bummer that oil pressure monitoring or datalogging in general hadn't made it into the car yet.

Andy, I'll talk to you later this week once you get to dig in to the motor a bit more.

Material defect in the rod bolt? Hydrogen embrittlement of said bolt?

Seems unlikely but who knows...

holy block batman!

Posted to Facebook an hour ago.

Mazda/Honda dropped, for a McLaren?

I'd say something SPECIAL surfaced today..

Tis true.

Ran out of time on the Miata to fix it right, so opted for something turn-key and quick as Plan B.

Good deal on the car means I can't really lose money on it (assuming I don't ball it up). And it gives me something fast to track when the other cars are laid up.

Andy,
Did you ever pinpoint the problem for this failure?

And any update on this kmiata?

No further progress on the diagnosis.

I put my stock TSX K24A2 in it a couple weeks ago and its running again. Wearing VR1's on 15x10's to fill out the fenders for now.

I've been kinda house-bound with Ann's knee surgery recovery, and the new shiny orange object has also been a distraction.

And to make matters worse, I just started buying parts for my ND to prep it for autocross.

Is this coming back for next year or is it dead?

I love the wider fender mod. If I have the money someday that's exactly how I would like to do it.

Andy has a McLaren to play with, so chances are slim lol!

It will get some love, yes. But as mentioned earlier, I now have four projects going on, so doling out time is a challenge.

Biggest hurdle at the moment is coming up with a headlight solution. The front tubbing was a touch too aggressive, and even the shorter NB2 headlights won't clear now. Plus, I have to completely re-do the CAI since that hole I was using got bent upwards to become the inner fender. There's a new center feed version of the Skunk2 Ultra intake manifold that might allow for better packaging w/o any performance loss.

For the moment, the CRX and 12C have been getting all the big-track love, while the ND gets used for Harris Hill and cone dodging. See the next GRM for more on that one.
--Andy

If you have a really good imagination you can see him driving it around Road Atlanta last weekend in this really poor quality video.

click to play

I wish there was a HQ link to some of these.

Try this and set it to full res HD:

I love ho the MPH has to play catch up down the back straight on the tracker :D

Thanks! That's a lot better. It is still somewhat blurry but I guess that is from wind buffeting the camera. It has been a couple of years since I went to the Toy Run. I need to get back to RA.

That HUD software is really awesome, I gotta get myself something like that.

.

No. I know that car (owned by Will Chan), but mine is naturally aspirated. More details at OneLapCRX.com

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